Dotnet Uno Testing

dotnet-uno-testing

Testing Uno Platform applications across target heads (WASM, Desktop, Mobile). Covers Playwright-based browser automation for Uno WASM apps, platform-specific testing patterns for different runtime heads, and test infrastructure for cross-platform Uno projects.

Version assumptions: .NET 8.0+ baseline, Uno Platform 5.x+, Playwright 1.40+ for WASM testing. Uno Platform uses single-project structure with multiple target frameworks.

Out of scope: Shared UI testing patterns (page object model, selectors, wait strategies) are in [skill:dotnet-ui-testing-core]. Playwright fundamentals (installation, CI caching, trace viewer) are covered by [skill:dotnet-playwright]. Test project scaffolding is owned by [skill:dotnet-add-testing].

Prerequisites: Uno Platform application with WASM head configured. For WASM testing: Playwright browsers installed (see [skill:dotnet-playwright]). For mobile testing: platform SDKs configured (Android SDK, Xcode).

Cross-references: [skill:dotnet-ui-testing-core] for page object model and selector strategies, [skill:dotnet-playwright] for Playwright installation, CI caching, and trace viewer, [skill:dotnet-uno-platform] for Uno Extensions, MVUX, Toolkit, and theme guidance, [skill:dotnet-uno-targets] for per-target deployment and platform-specific gotchas.

Uno Testing Strategy by Head

Uno Platform apps run on multiple heads (WASM, Desktop/Skia, iOS, Android, Windows). Each head has different testing tools and trade-offs.

Recommended priority: Test shared business logic with unit tests first. Use Playwright against the WASM head for UI verification -- it is the fastest UI testing path with the broadest coverage. Add platform-specific Appium tests only for behaviors that differ between heads.

Playwright for Uno WASM

The WASM head renders Uno apps in a browser, making Playwright the natural choice for UI testing.

Test Infrastructure

// NuGet: Microsoft.Playwright
public class UnoWasmFixture : IAsyncLifetime
{
    public IPlaywright Playwright { get; private set; } = null!;
    public IBrowser Browser { get; private set; } = null!;
    public IPage Page { get; private set; } = null!;

    private Process? _serverProcess;

    public async ValueTask InitializeAsync()
    {
        // Start the WASM app (dotnet run or serve the published output)
        _serverProcess = await StartWasmServerAsync();

        Playwright = await Microsoft.Playwright.Playwright.CreateAsync();
        Browser = await Playwright.Chromium.LaunchAsync(new BrowserTypeLaunchOptions
        {
            Headless = true
        });
        Page = await Browser.NewPageAsync();

        // Wait for Uno WASM app to fully load
        await Page.GotoAsync("http://localhost:5000");
        await WaitForUnoAppReadyAsync();
    }

    public async ValueTask DisposeAsync()
    {
        await Page.CloseAsync();
        await Browser.CloseAsync();
        Playwright.Dispose();

        _serverProcess?.Kill(entireProcessTree: true);
        _serverProcess?.Dispose();
    }

    private async Task WaitForUnoAppReadyAsync()
    {
        // Uno WASM apps show a loading splash; wait for the app root to appear
        await Page.WaitForSelectorAsync(
            "[data-testid='app-root'], #uno-body",
            new() { State = WaitForSelectorState.Visible, Timeout = 30_000 });

        // Additional wait for Uno runtime initialization
        await Page.WaitForFunctionAsync(
            "() => document.querySelector('#uno-body')?.children.length > 0",
            null,
            new() { Timeout = 15_000 });
    }

    private static async Task<Process> StartWasmServerAsync()
    {
        var process = new Process
        {
            StartInfo = new ProcessStartInfo
            {
                FileName = "dotnet",
                Arguments = "run --project src/MyApp/MyApp.Wasm.csproj --no-build",
                UseShellExecute = false,
                RedirectStandardOutput = true,
                RedirectStandardError = true
            }
        };
        process.Start();

        // Wait for server to be ready by probing the health endpoint
        using var httpClient = new HttpClient();
        var deadline = DateTime.UtcNow.AddSeconds(30);
        while (DateTime.UtcNow < deadline)
        {
            try
            {
                var resp = await httpClient.GetAsync("http://localhost:5000");
                if (resp.IsSuccessStatusCode) break;
            }
            catch (HttpRequestException)
            {
                // Server not ready yet
            }
            await Task.Delay(500);
        }
        return process;
    }
}

WASM UI Tests

public class UnoNavigationTests : IClassFixture<UnoWasmFixture>
{
    private readonly IPage _page;

    public UnoNavigationTests(UnoWasmFixture fixture)
    {
        _page = fixture.Page;
    }

    [Fact]
    public async Task MainPage_LoadsSuccessfully()
    {
        // Uno WASM renders XAML controls as HTML elements
        // Use AutomationProperties.AutomationId for selectors
        var title = _page.Locator("[data-testid='main-title']");

        await Expect(title).ToBeVisibleAsync();
        await Expect(title).ToHaveTextAsync("Welcome");
    }

    [Fact]
    public async Task Navigation_ClickSettings_ShowsSettingsPage()
    {
        await _page.ClickAsync("[data-testid='nav-settings']");

        var settingsHeader = _page.Locator("[data-testid='settings-header']");
        await Expect(settingsHeader).ToBeVisibleAsync();
        await Expect(settingsHeader).ToHaveTextAsync("Settings");
    }
}

Form Interaction Tests

[Fact]
public async Task LoginForm_SubmitValid_NavigatesToDashboard()
{
    await _page.FillAsync("[data-testid='username-input']", "testuser");
    await _page.FillAsync("[data-testid='password-input']", "P@ssw0rd!");
    await _page.ClickAsync("[data-testid='login-button']");

    // Wait for navigation after login
    var dashboard = _page.Locator("[data-testid='dashboard-title']");
    await Expect(dashboard).ToBeVisibleAsync(
        new() { Timeout = 10_000 });
}

[Fact]
public async Task TodoList_AddItem_AppearsInList()
{
    await _page.FillAsync("[data-testid='todo-input']", "Buy groceries");
    await _page.ClickAsync("[data-testid='add-todo-btn']");

    var items = _page.Locator("[data-testid='todo-item']");
    await Expect(items).ToHaveCountAsync(1);
    await Expect(items.First).ToContainTextAsync("Buy groceries");
}

Platform-Specific Testing

AutomationProperties for Cross-Platform Selectors

Uno maps AutomationProperties.AutomationId to each platform's native identifier:

<!-- Uno XAML -- works across all heads -->
<Page x:Class="MyApp.Views.LoginPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <StackPanel>
        <TextBox AutomationProperties.AutomationId="username-input"
                 PlaceholderText="Username" />

        <PasswordBox AutomationProperties.AutomationId="password-input"
                     PlaceholderText="Password" />

        <Button AutomationProperties.AutomationId="login-button"
                Content="Log In" />

        <TextBlock AutomationProperties.AutomationId="error-message"
                   Foreground="Red" />
    </StackPanel>
</Page>

Platform mapping:

• WASM: Rendered as data-testid attribute (Playwright selector)
• Android: Maps to content-desc (Appium AccessibilityId)
• iOS: Maps to accessibilityIdentifier (Appium AccessibilityId)
• Windows: Maps to AutomationId (WinAppDriver AccessibilityId)

Testing Platform-Specific Code

For code that varies by platform, use conditional compilation and separate test classes:

// Shared test -- runs on all platforms
[Fact]
public async Task Settings_ChangeTheme_UpdatesUI()
{
    await _page.ClickAsync("[data-testid='theme-toggle']");

    var body = _page.Locator("[data-testid='app-root']");
    await Expect(body).ToHaveAttributeAsync("data-theme", "dark");
}

// Platform-specific test
[Fact]
[Trait("Platform", "WASM")]
public async Task FileUpload_BrowserDialog_AcceptsFiles()
{
    // WASM uses browser file picker -- test with Playwright file chooser
    var fileChooserTask = _page.WaitForFileChooserAsync();
    await _page.ClickAsync("[data-testid='upload-btn']");
    var fileChooser = await fileChooserTask;
    await fileChooser.SetFilesAsync("testdata/sample.pdf");

    var fileName = _page.Locator("[data-testid='file-name']");
    await Expect(fileName).ToHaveTextAsync("sample.pdf");
}

Runtime Head Validation

Validate that the same UI logic works correctly across different Uno runtime heads using shared test logic with platform-specific drivers.

Shared Test Logic Pattern

/// <summary>
/// Abstract base that defines UI tests once. Concrete subclasses provide
/// the driver for each platform (Playwright for WASM, Appium for mobile).
/// </summary>
public abstract class LoginTestsBase
{
    protected abstract Task FillFieldAsync(string automationId, string value);
    protected abstract Task ClickAsync(string automationId);
    protected abstract Task<string> GetTextAsync(string automationId);
    protected abstract Task WaitForElementAsync(string automationId, int timeoutMs = 5000);

    [Fact]
    public async Task Login_ValidCredentials_ShowsDashboard()
    {
        await FillFieldAsync("username-input", "alice");
        await FillFieldAsync("password-input", "P@ssw0rd!");
        await ClickAsync("login-button");

        await WaitForElementAsync("dashboard-title");
        var title = await GetTextAsync("dashboard-title");
        Assert.Equal("Dashboard", title);
    }

    [Fact]
    public async Task Login_EmptyPassword_ShowsValidationError()
    {
        await FillFieldAsync("username-input", "alice");
        await ClickAsync("login-button");

        await WaitForElementAsync("error-message");
        var error = await GetTextAsync("error-message");
        Assert.Contains("required", error, StringComparison.OrdinalIgnoreCase);
    }
}

// WASM implementation
public class LoginTestsWasm : LoginTestsBase, IClassFixture<UnoWasmFixture>
{
    private readonly IPage _page;
    public LoginTestsWasm(UnoWasmFixture fixture) => _page = fixture.Page;

    protected override async Task FillFieldAsync(string automationId, string value) =>
        await _page.FillAsync($"[data-testid='{automationId}']", value);

    protected override async Task ClickAsync(string automationId) =>
        await _page.ClickAsync($"[data-testid='{automationId}']");

    protected override async Task<string> GetTextAsync(string automationId) =>
        await _page.Locator($"[data-testid='{automationId}']").TextContentAsync() ?? "";

    protected override async Task WaitForElementAsync(string automationId, int timeoutMs = 5000) =>
        await _page.WaitForSelectorAsync(
            $"[data-testid='{automationId}']",
            new() { Timeout = timeoutMs });
}

Key Principles

• Test shared logic with unit tests first. Uno's MVVM pattern means most business logic is testable without any UI framework.
• Use Playwright + WASM as the primary UI testing path. It is faster than mobile emulators and provides real rendering fidelity in a browser.
• Use AutomationProperties.AutomationId on all testable controls. It is the only selector strategy that works identically across all Uno heads.
• Separate shared tests from platform-specific tests. Use abstract base classes for shared test logic, concrete subclasses per platform.
• Add platform-specific tests only for platform-divergent behavior. File pickers, hardware buttons, gestures, and notifications differ across platforms; test these separately.

Agent Gotchas

1. Do not assume Uno WASM apps load instantly. The Uno runtime must initialize (mono WASM bootstrap), which takes several seconds. Always wait for the app root element before interacting.
2. Do not use CSS selectors for Uno WASM elements. Uno generates its own DOM structure; CSS classes are internal and unstable. Use data-testid (from AutomationProperties.AutomationId) exclusively.
3. Do not forget to build the WASM head before running Playwright tests. dotnet run builds on demand, but dotnet publish is needed for production-like testing. Stale builds cause confusing test failures.
4. Do not test mobile-specific features in the WASM head. File system access, push notifications, biometrics, and NFC are not available in the browser. Skip or mock these in WASM tests.
5. Do not run all platform tests in a single CI job. Each platform requires its own SDK (Android SDK, Xcode, WinAppDriver). Use separate CI jobs per platform with appropriate runners.

References

• Uno Platform Testing Documentation
• Playwright for .NET
• Uno Platform WASM Head
• AutomationProperties in UWP/WinUI
• Uno Platform GitHub